1. Field of the Invention
The present invention relates to a tire for trucks/buses that has an improved decoupling groove capable of preventing uneven wear of a shoulder rib while providing a proper grip to a shoulder, and more particularly to a tire for trucks/buses that has an improved decoupling groove capable of suppressing unbalanced wear of a shoulder rib, preventing side chipping of a tread, and enhancing durability of a belt.
2. Description of the Related Art
Heavy load tires, such as truck tires, bus tires and the like, have higher load capacity, wear resistance, and stiffness than car tires. Such a heavy load tire is formed with a decoupling groove between a tread and a shoulder. To prevent uneven wear of a shoulder rib, the decoupling groove is formed narrowly at an edge of the shoulder to maintain a proper grip of the shoulder.
In a conventional tire, a decoupling groove generally undergoes irregular wear or uneven wear which tends to occur on opposite outermost ribs 101a of a tread 101 as shown in FIG. 2. This is because the maximum friction is generally exerted on the outermost ribs 101a. In this regard, although the irregular wear can be suppressed by adjusting a shape of a tire casing, there is the possibility of failure in suppressing the irregular wear through shape adjustment of the tire casing due to external environmental conditions such as vehicle alignment, road conditions, etc.
To further improve wear resistance under such extreme conditions, the tire is provided with a decoupling groove 104 also called a sacrifice rib 105. In this case, friction on the outermost rib 101a is intentionally concentrated on the sacrifice rib 105, so that wear of the outermost rib 101a of the tread 101 can be suppressed by accelerating wear of the sacrifice rib 105.
Since the outermost rib 101a and the sacrifice rib 105 are separated from each other via the decoupling groove 104, not only is transfer of the irregular wear from the sacrifice rib 105 to the outermost rib 101a of the tread 101 suppressed, but also transmission of vibration or deformation generated during driving to the shoulder of the tread 101 via a side wall is suppressed as much as possible.
Two types of decoupling grooves are generally used for the conventional truck or bus tire: one is a vertical-type structure wherein the decoupling groove 104 is vertically formed in the outermost rib 101a of the tread 101 as shown in FIG. 3.
This type of the decoupling groove is typically designed to allow the sacrifice rib 105 to absorb the friction on the outermost rib 101a. Here, the sacrifice rib 105 has lower stiffness and more active movement than the outermost rib 101a under the same driving condition. As a result, increased friction and wear are concentrated on the sacrifice rib 105, so that the irregular wear can be prevented from being transferred to the outermost rib 101a adjacent the sacrifice rib.
The other is a side-type structure wherein the decoupling groove 104 is formed on a lateral side 102 instead of on the tread 101. The side type is functionally similar to the vertical type, but differs in that the decoupling groove 104 is formed on the lateral side 102 and has no sacrifice rib. In the side-type decoupling groove, contact pressure (i.e. vertical pressure) generated when an outward edge of the outermost rib 101 contacts the ground is discontinuously and largely decreased by the decoupling groove 104, which reduces friction between the outermost rib and the ground while suppressing wear of the outermost rib.
As described above, the two types of conventional decoupling grooves are first different in terms of position of the decoupling groove and function of suppressing uneven wear, and secondly are different in terms of a method of overcoming stone drilling.